1. Field of the Art
This invention relates to a joint pin lock mechanism or system for use on a pivotal pin joint which connects a pair of mechanical structural members pivotally relative to each other through a joint pin, and more particular to a joint pin lock mechanism which can lock a joint pin securely and safely in position in a fixed state against undesired rotational movements and against spontaneous axial movements as well if necessary.
2. Prior Art
In the manufacture of machines such as construction machines, for instance, it has been well known to connect two mechanical structural parts through a pivotal pin joint to permit pivotal movements relative to each other. As for example, shown in FIG. 10 is a hydraulic power shovel which employs pivotal pin joints of this sort. Basically, the hydraulic power shovel is constituted by a vehicular body having a crawler type base carrier 1 and an upper rotary body 2 which is rotatably mounted on the base carrier 1. Provided on the upper rotary body 2 is an operator's cab 3 and a front working mechanism 4 which is arranged to do predetermined jobs. The front working mechanism 4 usually includes a boom 5 which is lifted up and down, an arm 6 which is pivotally connected to the fore end of the boom 5 for swinging movements in a vertical direction, and a front attachment, for example, a bucket 7 which is pivotally supported at the fore end of the arm 6.
In the case of a hydraulic power shovel as shown, normally hydraulic motors are employed for driving the vehicular base carrier 1 and for rotation of the upper rotary body 2. In addition, the front working mechanism 4 are driven by hydraulic cylinders 8 to 10. The boom 5 is lifted up and down by a boom operating cylinder 8 which is connected between the boom 5 and the upper rotary body 2. Namely, one end of a cylinder tube 8a of the boom operating cylinder is connected to the upper rotary body 2 and a rod 8b which is projected from the other end of the cylinder 8a is connected to the boom 5. A cylinder tube 9a of the arm cylinder 9 is connected to the boom 5, and a fore end portion of its rod 9b is connected to the arm 6. Further, a cylinder tube 10a of the bucket cylinder 10 is connected to the arm 6, and its rod 10b is connected to the bucket 7. In connecting the cylinders 8a to 10a and rods 8b to 10b of the respective drive cylinders 8 to 10 in this manner, two mechanical parts at each connecting point are connected through a pivotal pin joint which permits relative rotational movements of connected mechanical parts about a joint pin and also permits separation of the two connected parts upon extraction of the joint pin whenever necessary.
In this regard, Japanese Laid-Open Patent Application H6-300033 discloses a pivotal pin joint construction which connects hydraulic cylinders 8 to 10 rotatably relative to and separably from a cooperating mechanical part. Shown by way of example in FIGS. 11 to 14 is the just-mentioned prior art pivotal pin joint construction which is used to connect a cylinder tube 9a of an arm operating cylinder 9 to a boom 5.
More specifically, shown in FIGS. 11 and 12 are a schematic outer view of the prior art pivotal pin joint and a sectional view taken on line Y--Y of FIG. 11, respectively. In these figures, indicated at 11L and 11R are brackets which are securely fixed to the boom 5 by welding or other suitable means. Supported between the brackets 11L and 11R (hereinafter a common reference numeral "11" is used for the two brackets for the convenience of explanation) is a connecting portion 12 of the cylinder tube 9a of the arm operating cylinder 9. A joint pin 13 is passed across the two brackets 11 through the connecting portion 12 thereby to support the arm cylinder 9 pivotally relative to the brackets 11 on the part of the boom 5. For this purpose, pin receptacle holes 11a and 12a are formed in the bracket 11 and connecting portion 12, respectively. A bush 14 is fitted in the pin receptacle hole 12a for sliding contact with the joint pin 13.
As the arm cylinder 9 is actuated, the arm 6 is turned up or down relative to the boom 5 to vary the angle between the arm cylinder 9 and the boom 5. At this time, the connecting portion 12 is subject to a force which acts to turn the connecting portion forcibly about the joint pin 13. If the joint pin 12 is caused to turn relative to the brackets 11 under the influence of the forced rotation of the connecting portion, it will hinder smooth movement of the boom 5 and could result in accelerated wearing of the joint pin 13 itself. Therefore, in addition to prevention of axial movements of the joint pin 13 which might result in disengagement from the connecting portion 12 and brackets 11, it is necessary to prevent rotational movements of the joint pin 13 relative to the brackets 11.
In the particular case shown, a joint pin lock structure 20 is formed on the pivotal pin joint upon inserting the joint pin 13. The joint pin lock structure 20 includes a collar portion 21 which is securely fixed to the joint pin 13 by welding and extended in a direction perpendicular to the axis of the joint pin 13. The just-described collar portion 21 function to lock the joint pin 13 in a fixed state in both rotational and axial directions.
In order to fix the collar portion 21 in position, a U-shaped anti-rotation plate 22 is securely fixed on the outer side of one of the paired brackets 11, for example, on the outer side of the bracket 11L, and the extended end of the collar portion 21 is arrested in a recess 22a of the U-shaped anti-rotation plate 22. By engagement of the collar portion 21 with the U-shaped anti-rotation plate 22, the joint pin 13 which is connected with the collar portion 21 is blocked against rotational movements. Further, the joint pin 13 is locked against movements in the axial direction by a stopper plate 23 which is provided with apertures (not shown) and fixed on the rotation blocking plate 22 by threading screws into screw holes in the rotation blocking plate 22 through apertures in the stopper plate 23.
The pin receptacle hole 11a is bored into the bracket 11L, and the anti-rotation plate 22 is fixed to the bracket 11, for example, by welding, in separate stages of a fabrication process. Consequently, difficulties are often encountered in fixing the anti-rotation plate 22 in position with strict accuracy relative to the center of the pin receptacle hole 11a, due to errors occurring under the influence of the heat of welding operation or errors occurring in a machining stage. In order to engage the fore end of the collar portion 21 of the joint pin 13 in the recess 22a of the anti-rotation plate 22 without failure despite such positioning or dimensional errors, it is necessary to form the recess 22a in a broader width as compared with that of the collar portion 22, providing a play or adjustment gap spaces .delta. on the opposite sides thereof to absorb possible dimensional or positioning errors when the collar portion 22 is placed in the recess 22a. In this manner, arrangements have to be made to ensure that the collar portion 21 can be fitted in the recess 22a without failure despite positional deviations of the anti-rotation plate 22 relative to the pin receptacle hole 11a.
As described above, it is inevitable to provide adjustment gaps 2.delta. between the recess 22a of the anti-rotation plate 22 and the collar portion 21 to compensate for errors in fabricating or machining stages although the anti-rotation function is impaired to a degree which corresponds to the width of the adjustment gaps 2.delta.. Besides, as the connecting portion 12 is turned repeatedly relative to the bracket 11L, the collar portion 21 is each time collided against wall surfaces of the recessed portion 22a of the anti-rotation plate 21. This eventually causes deformations and damages to the anti-rotation plate 22 and the collar portion 21 and as a result broadens the gap spaces to further deteriorate the anti-rotation function of the pin lock mechanism and accelerate wearing of the anti-rotation plate 22.